The present invention relates to a lithographic printing plate material which utilizes silver complex diffusion transfer process (DTR process) and in particular, to a lithographic printing plate material in which a polyester film coated with an organic copolymer composition for imparting hydrophilicity and for adhesion is used as a support.
A method of making lithographic printing plate which comprises imagewise exposing a lithographic printing plate material for DTR process, more particularly, a material comprising a support and, provided thereon, at least one silver halide emulsion layer and a nuclei layer containing physical development nuclei particles and then subjecting the exposed material to silver complex diffusion transfer development, thereby to form metallic silver image on the surface of the material is called "direct plate making method" and this method has the advantages in its simplicity and rapidness as compared with conventional plate making method which uses a lith film as an intermediate process, but has the defect in printability that only a small number of prints can be obtained. Under the circumstances, various improvements have been proposed.
The lithographic printing plate materials which are disclosed in Japanese Patent Kokoku No. 48-30562 and which have the above-mentioned defect have been considerably improved in printability as proposed in Japanese Patent Kokoku Nos. 51-15765 and 51-16803 and Japanese Patent Kokai Nos. 51-111103, 52-150105, 53-9603, 54-135002, 55-7704, 56-27151, and 57-86835.
On the other hand, as support, various supports are used as also mentioned in the above patent publications and plastics are mainly used for improving printability and inhibiting extension of plate or penetration of water thereinto during printing. Of the plastics, polyester films are mainly used which are superior in mechanical properties, dimensional stability, heat resistance, chemical resistance and transparency.
As well known, however, polyester films are generally high in crystallinity, chemically inert, excellent in chemical resistance and besides, highly hydrophobic because of having no hydrophilic group and so it has been difficult to attain satisfactory adhesion to hydrophilic photographic emulsion layer.
Hitherto, various attempts have been made in order to solve the above problem. One of them is to subject a polyester film to surface activation treatment such as chemical treatment, mechanical treatment, discharging treatment, flame treatment, ultraviolet ray treatment, high frequency treatment, plasma treatment, laser treatment, mixed acid treatment or ozone oxidation treatment and then directly coat a photographic emulsion layer thereon. These methods are proposed in U.S. Pat. No. 2,934,937 and 3,475,193, British Patent No. 1,215,234, and Japanese Patent Kokai Nos. 53-13672 and 55-18469. However, the thus surface treated polyester films are improved in adhesion to hydrophilic photographic emulsion layer, but are inferior in adhesion strength.
Another method comprises subjecting a polyester film to surface treatment to increase adhesion to hydrophilic photographic layer, thereafter providing a subbing layer of an organic copolymer composition and then coating a photographic emulsion thereon. This method can be roughly classified into the following two.
(1) A method of coating a composition comprising an organic solvent which is swelling agent or dissolving agent and an organic copolymer (hereinafter referred to as "solvent subbing method"). This method is disclosed, for example, in U.S. Pat. No. 2, 830,030, British Patent Nos. 772,600, 776,157, and 785,789, and Japanese Patent Kokai Nos. 50-1718 and 50-825.
(2) A method of coating an aqueous composition of organic copolymer substantially free from organic solvent (so-called latex) (hereinafter referred to as "aqueous subbing method"). This method is disclosed, for example, in Japanese Patent Kokoku Nos. 44-13278 and 45-10988, Japanese Patent Kokai Nos. 49-11118, 51-27918, 52-114670, 54-11177, 55-67745, 58-169145, and 59-77439.
The solvent subbing method of (1) has the problem of deterioration in properties of polyester film in subbing step and the problem in hygienic safety caused by the organic solvents and the problem of environmental pollution and now the aqueous undercoating method of (2) is increasingly employed.
However, when the method of (2) is applied to the lithographic printing material of Japanese Patent Kokoku No. 48-30562 referred to hereabove, no problem has occurred for printing of a small number of prints in initial time, but when printability has been improved and a large number of prints are to be made or when a special ink such as ultraviolet-curing ink is used for printing, peeling of photographic layer from support, so-called "peeling of film" occurs during printing and eventually printing becomes impossible. This is a serious defect. It is considered that this phenomenon of film peeling is caused by organic solvent in printing ink. There has not yet been found a subbing method which causes no peeling of film, though degree of peeling depends on kind of organic copolymer used in subbing layer or kind of subbing method. To find such subbing method is very important for lithographic printing plate which has polyester film as a support and which utilizes DTR process (especially for printing of a large number of prints).